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WATER WISE
Think before digging the earth
S. VISHWANATH
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Soil erosion in the case of mega constructions affects water aquifers
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— Photo: H. Vibhu
Cruel choice: When roads are dug up in the name of development, the water table goes down.
As we dig for underpasses, metros and basements for parking in our cities, let us spare a thought to the damage that is being caused by these actions to the most fundamental of natural resources — our soils and water. It takes years for soil to be created by weathering of the base rock and minerals. The humus created through organic material and microbial action then layers the soil and provides the nutrition for plants and trees. Soil, especially the top layer of it
, contain the highest amount of bio-diversity that exists on earth. When we dig and then pave what we dig we are irreparably damaging this bio-diversity.
Soil also has a better capacity than water to convert human and other waste to a nutrient. Phosphates and nitrates, for example, are better fixed by soil than water where they pollute.
When it rains, water infiltrates the top surface of the soil and percolates to reach the aquifer. The soil layer acts as a filter in the same way the skin of the body keeps the environment out. Soil and the weathered rock have porosity and hold water in different ways and generally for different purposes. Water in the soil usually is utilised by the roots of plants. Only when the soil moisture deficit is met and completed will water start to percolate down into the aquifer and recharge the ground water.
Channels
Trees not only take water from the soil and the weathered rock but also become channels for recharge through the roots. When trees are felled the soil is subject to erosion as well as the channels for groundwater recharge are impeded. This is one reason why we need trees in our cities.
For thousands of years the shallow aquifers have provided civilizations water mainly through open wells. While in many places the water table has fallen dramatically to render the open wells redundant, rainwater harvesting measures are also being taken simultaneously to recharge the aquifers. If we dig into the shallow weathered zone with our metros and our underpasses we not only prevent water from entering the aquifers but also take away the capacity for storage and impede flows. Decisions for such structures therefore need to factor in their impact on subsurface water.
Wrong practices
In Bangalore, while an underpass was being built steps had to be taken to drain away ground water through a horizontally drilled pipeline. Ground water , was seen as a potential flood-creating problem and investments were made to drain it away. In another case a multi-storeyed building constructing a huge basement struck water at about three metres below ground level and then resorted to large scale pumping to drain away this water. On the other hand the building itself needed to buy water for the construction process.
What does it mean for development and planning? A good layout plan or a good infrastructure plan would take a serious a look at its soil and groundwater interface and take measures to preserve and reinforce the positive characteristic of these. Ground cover would be used to the minimum and digging limited. Areas of rich soil potential would be left for bio-diversity. The weathered zone potential below the soil zone, to store water and be replenished, would be used to the maximum.
Water wisdom lies in realising the importance of the entire ecosystem that supports the availability of quality local water. Whatever we do to the soil impacts water directly or indirectly. Think twice before digging.
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